Stainless steel polishing



v scratches and blemishes.

Patented Feb. 8, 1949 umrao s'rA'r STAINLESS STEEL POLISHING Irvine C.Clingan, Baltimore, Md., minor, by

mesne assignments, to Armco tion, a corporation of Ohio Steel Corpora-No Drawing. Application March 31, 1944,

, Serial No. 528,959

3 Claims. '(01. 204-140) My application for patent is a continuation inpart of my copending application, Serial No. 523,572, filed February'23, 1944, and entitled Stainless steel polishin and the inventionrelates to stainless steel articles and products, and more particularlyto a method of electrolytically polishing the same, and to the resultantarticles themselves.

An object of my invention is the provision oi an eflicient and whollyreliable method for the rapid production of electrolytically polishedstainless steel articles and products.

A further object of my invention is the provision of a method for thecontinuous, mass production of bright-polished, high-carbon stainlesssteel articles and products.

A still further object of my invention is the provision of bright,electrolytically polished stainless steel articles and products includinthose of high-carbon quality.

Other objects in part will be obvious and in part pointed outhereinafter.

The invention accordingly consists in the art or process as describedherein, as well as the resultant product, the scope of the applicationof which is indicated in the following claims.

As'conducive to a clearer understanding of certain features of myinvention, it may be noted at this point that stainless steel is definedas an alloy comprising small amounts of carbon, from about 10% to 35% ormore-chromium, with or without separate percentages of nickel, and withor without supplemental additions of manganese, silicon. cobalt, copper,molybdenum, tungsten, vanadium, columbium, titanium, sulphur, or thelike,-.for.speci'al purposes, and a remainder which is substantially alliron except for incidental impurities.-. a

It is well known in the art that stainless steel in unpolished conditionhas a characteristic dull gray appearance, and that with properpolishing treatment the steel is finished to possess a brilliant,mirror-like surface. There are, in this connection, certain polishingmethods which involve mechanical treatment such as abrading, bufilng,-rubbing and the like. These methods, apart from yielding products whichare prohibitively expensive, are tedious and time-consuming, requireskilled labor, and frequent replacement of polishing equipment. Theyfall short ofgivinguniformly' polished products; and are unsatisfactorywhere peculiar .or intricate metal surfaces areencountered, or. wherepolished surfaces are-desired which are substantially free of A morerecent expedient for effecting a polish on stainless steel, namely,electrolytic-polishing, shows great promise from a commercial standpointas compared with the still widely used grinding, buffing, and likemechanical polishing methods. It has been demonstrated that electrolyticpolishing methods are far more simple, and are more rapid and economicalof performance. The resulting electrolytically polished products aremarketable at lower prices, yet possess greater brilliance and beautythan mechanically finished products, and are more even and uniform offinish.

While the art of electrolytic polishing does represent an exceptionallygreat advancement in the field of stainless steel finishing, the artstill is relatively new and as such leaves much to be sought in way ofimprovement. One difliculty of the. art hasbeen that of providing auniform electro-polish on stainless steels having a carbon content of0.25% or more. The steels which come within this classification are veryerratic in their response to conventional electrolytictreatment; thequality of finish obtainable being anywhere from flat gray to bright inappearance depending upon the specific high-carbon quality of the steeland the condition of heat treatment thereof.

There are electrolytic polishing processes which are objectionable inthat the bath employed has poor electrical conductivity and evaporates.Evaporation of essential ingredients causes a dilution of the bath withrespect to these ingredients, thus requiring frequent replenishing. Insuch cases the operating conditions for obtaining best polish aredifficult to maintain with the result that finished products are likelyto exhibit surfaces with etching or lack of polish.

Certain-heretofore known electrolytic polishingprocesses areinsufliciently rapid in eflect to permit their practical use forcontinuous polish-' ing treatment as distinguished from batch operation.At best, in adapting the process for such uses, long vats are necessaryto give prolonged electrolytic polishing action, large quantities ofsolution are required to fill the vats, and other complications, such asthe need for numerous anodic contacts for obtaining efiective feedingalong the length of vat, together with the-problems of heating andmaintenance of proper temperatures of solution, all enter. Even withelonated vats, continuous feeding of products through the bathessentiallyis kept slow in order toachieve-proper polishing treatment. v

'An outstanding object of my invention acaceaoae cordingly is theprovision of a process for the continuous electrolytic polishing of awide variety o stainless steels including those of 0.25% minimum carboncontent quality in hardened or unnardened condition, which methodensures the rapid obtainment of a bright polish while employing a bathand related operating conditions that are practical, reliable, andsimple to maintain.

Referring now more particularly to the practice of my invention, Ibright-polish stainless steel articles and products electrolytically, asfor example wire, rods, sheet, strip, and the like by moving the samelineally thru an acid bath consisting approximately, by weight, of 50%to 70% concentrated ortho-phosphoric acid (specific gravity 1.7), to 30%concentrated sulphuric acid (specific gravity 1.84), 1% to 20%. butylcarbitol (diethylene glycol mono-butyl ether), and water, this latterranging from amounts which are incidental to the acids and butyl'carbitol up to a-remainder not exceeding approximately 39% total weightof solution. While so moving the products anodic contact is preserved asby way of a stationary anode contact maintained beneath the surface ofthe bath. During the polishing treatment, I maintain a temperature oftreating bath within the approximate range of 125 F. to 165 F., and acurrent density of about 5 to 12 or more amperes per square inch ofproduct surface immersed in the bath.

The process is suited for the continuous brightpolishing of stainlesssteel including either the high-carbon or low-carbon steels in variousconditions of heat treatment or hardness beginning in soft and extendingthrough hard as incident to annealing, quench hardening or precipitationhadening. A wide variety of straight-chromium or chromium nickelstainless steels including the 18-8 chromiummickel grades are rapidlypolished using my treatment. In general, a bright, lustrous polish isachieved on the steel in a period of time as short as one-half minute,de pending somewhat upon the initial surface condition and the grade orquality of steel.

As illustrative of the practice of my invention, I treatbright-annealed, low-carbon 18-8 chromium-nickel stainless steel wire byfeeding or reeling the same directly and continuously from an annealingfurnace through an electrolytic polishing unit where the wire issubjected to polishing treatment. The polishing unit comprises asuitable container such as an open tank, having a lead or other acidresistant lining in which is provided an electrolyte solution containingby weight, for example: approximately 56% orthophosphoric acid (85%concentrated quality having a specific gravity of 1.7) about 27%sulphuric acid (98% concentrated quality having a specific gravity of1.84), about 7% butyl carbitol, and the remainder substantially allwater. The wire is fed or reeled through the solution over spaced anodiccontacts or rolls at a rate, for example, of six feet per minute whilemaintaining a current density of about 5 amperes per square inch ofimmersed wire surface, and a bath temperature of about 140 F. Preferablythe contact between the moving work and the anodic contacts is hadbeneath the surface of the bath. The anodic contacts as well as thecathodes employed illustratively are of copper. Under such conditions athoroughly bright, lustrous polish is obtained on the wire in aboutone-half minute, which means that the effective length of solution tankneed not be over 2 to 4 feet. For greater 4 speeds of reeling, ofcourse, the length of tank should be increasedunless higher currentdensities or temperatures are employed, either of which alternativeswould be wholly permissible within the broad limits mentionedhereinbefore. It will also be understood that the composition of bathmay be varied with good results within the broad composition limitsspecified hereinbefore.

, From the electrolytic bath the polished wire preferably is fed orreeled through a washing fluid such as clean water and thence ontoreels, after which the product is ready for use or sale. The wirepossesses a mirror-like surface which is free of scale, is evenlypolished, and highly attractive.

My electrolytic polishing process is successfully practiced on stainlesssteel wire, rod, sheet, strip and the like of widely differing qualityand consistently gives uniformly polished stainless steel surfaces. Theelectrolytic polishing process which I provide is, moreover, rapid andeconomical of performance and is quite adaptable to continuous massproduction of polished high-carbon or lowcarbon stainless steel productsof outstanding quality. Polishing is had as a part of a continuouswire-drawing or sheet-reeling or strip-reeling operation without delayor other sacrifice in the speed and efficiency of those operations.

In my electro-polishing process as described above the electrolytesolution employed is reliably stable over a wide range of effectivetemperatures which are convenient to maintain, and will support currentdensities which are admirably suited for rapid polishing treatmentwithout requiring frequent replenishing due to excessive evaporation. Itis also important, in way of advantage, that the polishing equipmentnecessary in my continuous process is cheap and readily available, iscompact requiring a minimum of space for installation, and afterinstallation is easily operated and maintained.

Thus it will be seen that there is provided in this invention, acontinuous process of electrolytically polishing stainless steels ofvarious qualities in which the various objects hereinbefore notedtogether with many thoroughly practical advantages are successfullyachieved. It will be noted that the process gives in a simple andeconomical manner, evenly polished stainless steel products which arefree of pits and other surface blemishes and which possess outstanding,lustrous beauty. It will Toe noted further that the process isinstrumental to the rapid achievement of an electrolytic polish of highquality through the use of an electrolyte of maximum stability, whichelectrolyte permits the use of high current densities and a wide rangeof operating temperatures.

As many possible embodiments may be made of my invention and as manychanges may be made in the embodiments hereinbefore set forth, it is tobe understood that all matter described herein is to be interpreted asillustrative and not as a limitation.

I claim:

1. In the rapid and continuous production of polished stainless steelwire, rods, sheet and strip having about 10% to 35% chromium, at leastabout 0.25% carbon and the remainder essentially iron, the art whichcomprises, establishing anodic connection to the said wire, rods, sheet.or strip, and lineally moving the same through an acid bath consisting,by weight, of about 50% to 70% concentrated ortho-phosphoric acid (sp.gr.

1m, about 10% to 30% concentrated sulphuric carbon content of about0.25% and the remainder l essentially iron, the art which comprises,axially moving the product through an acid bath consisting, by weight,of 50% to 70% concentrated ortho-phosphoric acid (sp. gr. 1.7), to 35%concentrated sulphuric acid (sp. gr. 1.84), 1% to diethylene glycolmono-butyl ether, and any remainder substantially all water, and whilemoving the same through said bath preserving electrical contact to theproduct by way of a stationary anodic contact and maintaining a. cur- 20,rent density of at least about 5 amperes per square inch of productsurface and a bath temperature between about 125 F. and 165 F.

3. In the rapid and continuous production of polished stainless steelwire, rods, sheet and strip having about 10% to chromium, about 0.25%minimum carbon content, and the remainder essentially iron, the artwhich includes moving the same lineally through an acid bath consisting,by weight, of about 56% concentrated ortho- 30 phosphoric acid (sp. gr.1.7), approximately 27% concentrated sulphuric acid (sp. gr. 1.84),about 7% diethylene glycol mono-butyl ether, and the remaindersubstantially all water, while mainsheet or strip giving a currentdensity of 5 to 12 amperes per square inch of product surface and whilepreserving a bath temperature of F.

to F., a mirror-like surface being achieved in about .5 to 1.5 minuteimmersion in the bath. I

IRVINE o. CLINGAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,315,695 Faust Apr. 6, 19432,330,562 Drummond et al. Sept. 28, 1943 2,334,698 Faust Nov. 23, 19432,348,517 Beckwith May 9, 1944 2,349,843 Beckwith May 30, 1944 FOREIGNPATENTS Number Country Date 682,248 Germany Oct. 20, 1939 OTHERREFERENCES The Iron Age, Jan. 11, 1940, pages 22 through 26.

Transactions of The Electrochemical Society," vol. 78 (1940), pages 265through 274; vol. 82 (1942) pages 227 through 239. Steel, June 17, 1940,pages 73 and 74.

Proceedings of The American Electroplaters Q Society," 1941, pages 104through 112; 1946, pages 62 and 63.

The Alloys of Iron and Chromium," by Kinzell taining anodic contact withthe said \vire, rods, 35 9t 1701- II (1940). P

